A background art will be described by way of a hydraulic shovel, for example.
As illustrated in FIG. 9, a hydraulic shovel includes a lower propelling body 1, an upper slewing body 2 that is rovolvably mounted on the lower propelling body 1, a work attachment (excavator attachment) 3 attached to the upper slewing body 2, and a cabin 4.
An engine room 6 formed of an engine cover 5 is provided at the back of the upper slewing body 2. An engine 7 and related devices thereof are accommodated in the engine room 6.
One disclosed in Patent Document 1 is known as a structure for discharging exhaust gas from the engine 7 and air that has cooled a heat exchanger to an outside of the engine room 6. This known technique will be described with reference to FIG. 10. FIG. 10 is a schematic view of a cross-section of the engine room 6 when seen from a rear side of the engine room 6.
A cooling fan 8 driven by the engine 7 and a heat exchanger 9 such as a radiator are provided in the engine room 6 on one end side of the engine 7. An intake opening 10 is formed in a portion on a side of an upper wall of the engine cover 5 where the fan 8 and the heat exchanger 9 are set, and a discharge opening 11 is formed in a portion on the opposite side of the upper wall. Outside air is introduced into the engine room 6 through the intake opening 10 with rotation of the fan 8 and passes through the heat exchanger 9, and air after cooling (hereinafter referred to as discharge wind) is discharged from the discharge opening 11.
On the other hand, a silencer (muffler) 12 is located on the other end side of the engine 7. The exhaust gas emitted from the engine 7 is discharged to the outside through the silencer 12 and an exhaust gas pipe (tail pipe) 13 connected to the silencer 12.
Here, since the exhaust gas is hot (for example, 500° C.), the exhaust gas deteriorates ambient temperature environment if the exhaust gas is directly discharged to the outside through the exhaust gas pipe 13. Moreover, in a configuration where the exhaust gas and the discharge wind are discharged as they are, the leakage to the outside of operating noise such as engine sound, exhaust sound, and discharge wind sound increases.
Therefore, in the known technique, a cylindrical duct 14 is provided at a position of the engine room 6 below the discharge opening 11 so as to extend in the up-down direction in a state where an upper end of the duct 14 is open to the discharge opening 11, and a lower end of the duct 14 is open to the inner side of the engine room 6. A distal end portion 13a of the exhaust gas pipe 13 is bent upward at the lower side of the duct 14 so that the distal end portion 13a is inserted into the duct 14 from the lower end of the duct 14.
By doing so, the discharge wind and the exhaust gas are guided into the duct 14, and both are mixed in the duct 14, whereby the temperature of the exhaust gas is decreased. After that, the discharge wind and the exhaust gas are discharged to the outside, and operating noise in the duct is reduced.
However, the pressure and the flow rate of the exhaust gas are greatly different from those of the discharge wind. Specifically, the pressure and the flow rate of the exhaust gas are higher than those of the discharge wind. Thus, it is naturally difficult for the exhaust gas and the discharge wind to mix with each other. Further, the known technique has a configuration in which the distal end portion 13a of the exhaust gas pipe 13 is inserted upward into the duct 14, and the exhaust gas is emitted from an opening (that is, intensively from one point) of the distal end portion 13a in the same direction as the discharge wind in the duct 14. Due to this, the mixing efficiency of the exhaust gas and the discharge wind worsens. Thus, the effect of decreasing the temperature of the exhaust gas is low.
Moreover, since the exhaust gas is discharged from the opening of the distal end portion 13a of the exhaust gas pipe 13 straightly toward the discharge opening 11, the reduction effect of the exhaust sound in the duct 14 also decreases.
Patent Document 1: Japanese Patent Application Publication No. H3-229907